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PCAP analysis: zeek

·329 words·2 mins
Table of Contents

Introduction
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Zeek is a powerful open-source network analysis framework designed for security monitoring and traffic analysis. Unlike traditional packet analyzers, Zeek operates at a higher level, interpreting network protocols and generating detailed logs about network activity.

Zeek is widely used to gain insights of network behavior, anomaly detection, and automating incident response. It’s scripting capabilities allow users to customize analysis process and extract meaningful data from large set of PCAP files.

Why use Zeek for PCAP analysis?

  • Protocol Awareness: Zeek understands dozens of network protocols, providing rich context beyond raw packet data.
  • Automated Logging: It automatically generates structured logs (e.g., connections, DNS, HTTP, SSL) for easy review and further processing.
  • Extensibility: Zeek’s scripting language enables custom detection and analysis workflows.
  • Scalability: Suitable for both small captures and large-scale network monitoring.

In this post, we’ll investigate how Zeek can be used to efficiently analyze PCAP files and extract actionable information for network security and troubleshooting.

Installing Zeek
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You can get latest version of zeek from https://zeek.org/ if you want to compile it from source. I would recommend to use ready made binaries which are available for most common distros.

Basic Usage
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In this article, we’ll focus on using Zeek to analyze PCAP files that have already been captured. While Zeek is capable of monitoring live network traffic, my typical workflow involves working with saved PCAPs.

Now that we have Zeek installed, it time to take it to the testrun.

  1. Key Log Files and Their Meaning

    • conn.log
    • dns.log
    • http.log
    • ssl.log
    • Notice.log

  2. Filtering and Extracting Data

    • Using Zeek scripts for custom analysis
    • Example: Extracting HTTP requests

  3. Automating Analysis

    • Batch processing multiple PCAPs
    • Integrating Zeek with other tools

  4. Practical Example

    • Step-by-step walkthrough: Analyzing a sample PCAP with Zeek
    • Interpreting results

  5. Tips and Best Practices

    • Performance considerations
    • Security implications

  6. Conclusion

    • Summary of Zeek’s strengths for PCAP analysis
    • Further resources

That covers the fundamentals of network traffic capture and analysis. These techniques form the foundation for deeper network security analysis and troubleshooting.